Liquid control mechanism



Dec, 11, 1945.

F. C. MOCK LIQUID CONTROL MECHANISM Filed April 15, 19 38 2 Sheets-Sheet 2 INVENTOR Y FRANK C. Mac/a ATTORNEY Patented Dec. 11, 1945 LIQUID CONTRQL MECHANISM FrankC. Mock, South Bend, Ind., asslgnor to Bendix Products Corporation, South Bend,

Ind., a corporation of Indiana 7 Application April 15, 1938, Serial No. 202,206

17 Claims.

This invention relates to fuel feeding systems for internal combustion engines and more particularly to devices or control mechanism in such systems for increasing the ratio of fuel to air supplied the engine during periods of high power operation. This application is a continuationin-part of my applications Serial Nos. 118,718

and 171,461, filed January 2, 1937, and October One of the principal objects of the invention is to provide an accurately metered fuel supply whereby the fuel and air ratio can be maintained within very close limits and at desired values throughout the range of engine operation.

Another object of the invention relates to'the provision of an improved economizer control to vary the richness of the mixture underdifierent operating conditions. The economizer controlis particularly desirable in engines equipped with superchargers and serves primarily toincrease the richness of the mixture as the engine approaches full power operation.

A further important object of the invention relates to the provision of a fuelflow economizer subjected to the fuel metering differential pressure of the normal fuel supply to the engine for controlling the supply of supplementary fuel to the engine;

Other desirable features and characteristics of the present invention relate to the provision of a fuel flow control mechanism influenced by air pressure at spaced points in the induction passage of the carburetor or manifold and by fuel pressure at spaced points in the system; the use of an improved fuel valve mechanism controlled by said air and fuel pressures; the use of an improved combination of manual .and automatic 1 control of the supply of fuel to the engine. A further object of the invention relates to the modification of the normal and supplemental fuel suppliesin accordance with variations in the barometric pressure of air supplied to the engine. While a principal utility of the invention is in connection with aircraft engines, it is,also applicable to engines of other types or to other uses template the employment of any structures, arrangements, or modes of operation that are/ properly within the scope of the appended claims.

Figure 1 is a diagramillustrating the principles of the invention in a schematic way;

Figure 2 is an enlarged partial view in section of the diaphragm-balanced fuel inlet valve of Figure 1; v

Figure 3 is a partial view in section illustrating a modified form of balanced inlet valve.

Referring first to Figure 1; a main air intake conduit Ill leads to a rotary blower or supercharger I2 of an internal combustion engine which may be of any desirable type. The conduit I0 is controlled by a throttle l6 which is operated by a rod l8 extending from the pilot's cockpit. The pilot thus controls directly. theair charge of the engine while the fuel charge is automatically controlled by the apparatus hereinafter described in detail. Anterior to the throttle is a venturi ll! of any suitable contour. In some cases a second supercharger may be employed to supply air at higher than atmospheric .pressure to the entrancezll of passage'lll, and

- at the entrance, which is in such cases usually referredto as a scoop.

An instrumentality such as the blower I2 is not essential to the invention, but is here own as representing approved practice in aircraft enwhere fuel is to be supplied vunder more or less analogous conditions.-

The characteristics and advantages of the invention are further sufficiently referred to in connection with the following detail. description of the accompanying drawings, which represent certain preferred embodiments. After considering these examples, skilled persons will understand that many variations maybe made without departing from the principles disclosed; and I congines, and serves to or assists in atomizing and properly distributing'fuel introduced into the air line in the manner presently referred to. The blower discharges into a generally annular chamber l5 from which'pipes lead to the intake ports of the various cylinders, as usual in this type of engine. 1

It is to be understood that the entire air passage between the throttle and the engine intake ports represents broadly an intake manifold, and the term is to be-so construed in this speciflca-. tion. Any known or suitable fuel pump, capable ofdelivering jfuel under positive pressure, is provided, that shown being of the sliding vane type and comprising a rotor 22 slidably carrying a set of vanes 23 and rotatably mounted in a casing 24.

- The casing has a fuel inlet 25,7,an outlet 28', and a 'rbtum bypass l0 controlled by a pressure responsive valve 42. so as to maintain a substantially constant outlet fuel pressure, in the known manner. The pump thus delivers fuel to passage 26 and thence into annular chamber 56, through ports 59, past a tapered poppet or lift type of valve I09 which seats at III, into pressure chamber 28, through fixed metering orifice 29, an adjustable metering orificetfi, into chamber I21 and through passage 32 to a discharge jet 30 positioned in the conduit I posterior to the throttle.

The discharge Jet 30 is provided with a valve 96 opening away from the manifold and connected to a flexible diaphragm 39. Fuel pressure entering through the pipe 32 acts on one face of the diaphragm 39 tending to open the valve 36, and is opposed by a spring 30. Since manifold vacuum is effective on valve stein 36 merely to the extent of its application on an area equivalent to that of the valve orifice whereas the fuel pressure is effective to the extent of its application on the relatively large area of the diaphragm 39, the fuel discharge pressure is practically unaffected even by large changes in manifold vacuum. The relatively large. diaphragm area also enables the valve to change from a relatively closed position to a wide open one (to give low and high rates of fuel discharge) with but a slight change in discharge pressure. This relatively constant pressure feature aids in obtaining accurate metering under variable operating conditions. A fixed stop 9? is preferably provided to limit opening of valve 36 to prevent damage in case of backfire or the like.

A second pressure chamber as is positioned adjacent chamber 28 and is separated therefrom by a flexible diaphragm 46 which is preferably of the type having no elastic reaction to stress, comprising a fabric sheet secured at its outer edges and having its central portion secured between a pair of disks 98. The disks 98 are in turn securedto a rod 50 which terminates at its the diaphragm assembly hereinafter described.- The parts are thus free to float to align them-.7

selves, thereby decreasing side pressure on the rod or valve which might cause binding.

As is best shown in Figure 2, the valve I09 is loosely slidable in a bore of a valve cage I HA and is adapted to seatat III to control the flow of fuelinto chamber 28. Valve I09 is carried by a plug H3 threaded on the valve stem I01 and should preferably be adjusted to seat when the diaphragm assembly hereinafter described is in the neutral position. The valve assembly is held in position by means of an outer nut H5 which maybe removed to take the assembly apart without disturbing the adjustment of the poppet valve on the valve stem. A-diaphragm Ill is secured to the valve I09 and to the cage IIIA. A passage II1A communicates the fuel chamber- 28 with the space to the right of the dia-'.

valve I09 and to seal any leakage of fuel from annular chamber 54 past the free fitting valve. The pressure of the fuel in chamber 28 acts to the right on the valve I08 over anarea v members BI adjacent the diaphragms and 00 of equal to the efiective area of the seat III and, by means of passage IIIA, to the? left on diaphragm III over an equal area thus balancing the effect of the pressure in chamber 28. The high pressure fuel in chamber 54, due to the free machine fit of valve I09 in the bore of cage IIIA, leaks past the valve I09 andvacts to the left on the valve I09 and to the right on diaphragm I ii.

The unbalanced force normally resulting from the differential pressure across a poppet valve is thus eliminated.

It may be noted that if a slide or sleeve type of valve were used the balancing diaphragm IIl would be unnecessary; however, such a valve requires a'very accurately lapped fit in order to regulate the fuel flow at low rates of flow corresponding to idle, and the slightest deposit of gasoline gum or a fine particle of dirt would cause such asleeve valve to bind and interfere with the operation of the device.

A leaf spring I I9 engages the socket I03 to urge the valve assembly toward the open position to provide an enrichment at idling speeds as will be described hereinafter. The force of the spring urging the valve toward open position may be varied by means of an adjusting screw I2I. The spring is preferably of such design that it acts on rod 50 and valve I09 only when the said valve is in a nearly closed position. The flange of collar I03 moves away from and is completely free of any effect of the spring at any substantial valve opening. The spring II9'is carried'by a gasket which engages the outer edge of the diaphragm 06 and when'theshell surrounding the valve mechanism I09 is removed the spring H9 remains in position, whereby it is possible to check the adjustment of the valve and valve assembly. r

The chamber 54 is preferably connected to the top of the fuel tank, not shown, by a pipe 59 controlled by a float valve 55 to vent back to the tank any air or vapor entrained by the pump.

Adjacent the chamber 44 is a chamber 50, separated therefrom by a small diaphragm '58, which merely serves the purpose of a leakless stufiing box. A second large diaphragm 00 separates chamber 56 from another chamber 62, and rod 50 is connected to the disks 64 of this diaphragm in the same manner as to those of diaphragm 96, A second stufling box diaphragm 66 is secured to the end of rod 50 and separates the chamber 62 from a chamber 68 positioned ad;|a--

cent thereto.-

The sealing diaphragms 50 and are preferably made of Duprene, synthetic rubber or other suitable material and are formed with annular grooves as c early shown to give a rolling action against the confining walls. It will be observed that the effective area of the diaphragm is unchanged regardless of the position to which it is interfere with the proper operation of the parts to which the diaphragm is attached are. thereby avoided. To facilitate assembly of the parts, the diaphragms may be formed with thickened attaching flanges while the working sections remain thin.

In order to balance out the unavoidable pressubstantially the same diameter as the flat central portionsof the diaphragms on the low pressure sides thereof. The diaphragms are formed with deep annular grooves as shown, the sides of which lie respectively against the members 8| and outer circular confining walls. Due to this construction and the diiferential'in fluid pressure which exists on the two sides of the diaphragms, the grooves in the diaphragms maintain a sub stantially constant effective radius as the rod 58 moves, so that the effective areas thereof remain constant regardless of movement of the rod 58 The same construction is preferably followed in I connection with the diaphragms l8 and 88 by roviding circular flanges 48 and 85 on the plates 48 and 84 respectively. This is 'an important feature since it enables the diaphragms always to exert the same force in response to equal pressures regardless of the deflection of the diaphragms. It will be observed that the end of the rod 58 is rounded to minimize friction and to permit it to seeka nonbinding position.

A small venturi I4 is positioned in the intake conduit I8 concentrically-with the venturi I8 and is formed with an annular opening I8 substantially at'its throat which is connected through a passage I8 with chamber 58. A small bypass 83 may if desired interconnect the passage I8 with the induction passage posterior to the throttle I8. Aslmilar passage 88 leads from chamber 82 to an annular chamber 82 formed in the venturi I8 and communicating with the inlet end of theconduit I8 through a. series of tubes 8| so as to be subjected to the pressure of the incoming air. The tubes 8| project out a substantial distance so that any rain or the like washing up the walls of the air conduit I8 will flow around enter the chamber 82.

The basic principles of operation of the inventhem and will not close valve I88, thus opposing the force on rod 88 created by the depression at venturi II.

A summation of forces acting onthe rod 58, neglecting the spring II8 which has no effect except at very small flowss'corresponding to idling range, will show that the rod 58 will adjust itself to a point of equilibrium such that the differential across the fuel metering orifices is equal to the differential pressure between air scoop and venturi. If now, the pressure of fuel delivered by ,pump 22 is increased, as by faulty pump action, the pressure in chamber 28 will increase, which will cause valve I88 to move toward closed position thereby restoring the fuel metering differenl5- tial pressure to its original value. If the engine speed is decreased, by a change in the propeller pitch or from any other cause, the rate of air flow through venturi I4 decreases, decreasing the differential pressure acting on diaphragm 88, causing valve I88 to move toward closed position and thus decreasing the fuel flow to compensate for the decreased rate of air flow which initiated the adjustment. The rate of fuel fiow is directly increment of force to the normal venturi action tion thus far'described arehere introduced in pressure is thus created between the air scoop and a the venturi, the amount of which is a function of,

the rate of air iiow. This differential in pressures acting in chambers 88 and 82 creates a net force tending to move rod 88 to the right in a direction to open valves I88. If this force were unopposed the. rod 88 and valve I88 would move to the extreme right. As valve I88 opens, however, fuel which is supplied under pressure to valve cham berlil, will flow into.the unmetered-fuel chamber 28, through the metering orifices, into the metered-fuel chamber 44, and thence to the dischargeje't 34 as previously described. A differential in pressure between chambers 28 and I4 is therefore created which is equivalent to the pressure drop across orifice 29 and passage 38 and Is a function of the rate of fuel flow therethrough. Since the pressure in chamber 44 is maintained within relatively narrow limits by the action of jet 34, opening of valve I 88 will increase the pres sure in chamber 28 (due to decreased throttling.

loss across said valve) thereby increasing the. differential pressure across the metering orifices and increasing the rate of fuel flow. 'The different al in pressure between chamber 44 and chambers 28 and 88 will exert a force on rod 58 tending to move it to the left or in a direction to tending to open the valve I88 and thereby requiring an increased pressure differential across diaphragm 48 to balance the forces on rod 58. This results in increased fuel flow and a richer mixture for idle operation.

The bypass 83 interconnecting the passage 18 with the induction passageposterior to the throttle I 8 introduces a net force operating on rod 88 it is possible to use a leaner mixture at'wide open throttle than is used at part throttle.

The passage 88 is controlled by a capsule or aneroid 84, shown in Figure l as a sealed, corrugated bellows which carries a valve member 88 which tends'to open passage 88 at high barometric pressures (as at groundor sea level) and to close the same at low pressures (as at high altitudes). A calibrated passage 88 connects the lower portion of chamber 82 to the passage I8. Passage 88 is sufliciently small in comparison with passages 18 and 88 that when valve 88 is open, air flow through passage 88 is not effective in materially altering the pressures existing in chambers 82 and 58. As altitude is gained, valve 88 moves toward closed position under action of the bellows 84, flow of air from chamber 82 into passage 88 is thereby restricted and the air flow from passage 88 through passage 88 becomes more effective in reducing-the pressureexisting' in chamber 82, thus decreasing the differential pressure acting on diaphragm 88 and tending to closevalve I88 and lean out the mixture as desired with increase in-altitude. .serves as a drain for any moisture collecting in chamber 82. I

To guard against the building up of-a differ;-

ential of fluid pressures between chambers 58 and r 82 which might prevent the rod 58 from actuat ing the valve I88 when it is desired to start the engine, a small bleed orifice 85'may be employed Passage 88 also to interconnect the chambers 56 and 62. It will be understood of course that the orifice 85 coin chamber I21 above the chamber M. ,A valve I25 controls the by-pass and is urged toward the closed position by a spring I29. The valve may be The bellows 84 is preferably only partially evacuated so that it will be responsive to changes in temperature as well as pressure, the amount of temperature response being controlled by the degree of evacuation. As the temperature of the air entering the air scoop increases, bellows 84 will elongat slightly, moving valve 86 to a position to restrict the passage at, reducing the pressure in. chamber 62, and thereby reducing -the pressure differential across the diaphragm 66. Consequently the fuel fiow will be slightly reduced to provide a leaner mixture as the inlet air temperature rises.

It is desirable to design spring H9 and bypass '83 to give an excessively rich idling mixture and then use valve 90, which is throttle connected through bellcrank 92 and link 9% and arranged to move into passage 30 at closed throttle, to restrict the flow of fuel through passage 30 so as to obtain the desired idle richness. The valve 90 can be given any desired configuration to provide the desired rate of fuel flow at closed as well as substantially closed throttle. Valve 90 is drawn clear of passage 30 as the throttle valve I6 is opened so that during normal operation the valve 99 occupies substantially the position shown and does not affect the fuel flow.

The port 39 may further be controlled by a plunger I015 controlled manually from the pilot's assembly I3 I.

urged toward the open position by a diaphragm A spring I33 inthe diaphragm chamber I35 .urges the diaphragm in the. direction to open the valve I against the spring I29. The spring I33 may be adjusted to seat the valve I25 at any predetermined value. The rate of valve opening is of course a function of the differential forces exerted by the springs I29 and I33 and the differential in the fuel pressures on opposite sides of the diaphragm I3I.

The diaphragm I8! is subjected on the right side to the metered fuel pressure in the chamber I27 and on the left side to the pressure of the unmetered fuel in the diaphragm chamber I35, a conduit I37 being employed in the form shown to transmit the unmetered fuel from the chamber 28 to the diaphragm chamber I35. A small vent I39 serves to permitthe escape of any air from the chamber E35, which might be trapped in seat through a linkage I06 to provide either a rich or lean mixture. When the end of the plunger ltd is projecting into the port 30, as shown, the flow of fuel is restricted and a lean mixture results. To obtain a richer mixture the pilot may operate linkage I06 .to withdraw the plunger Wt completely from the port 38 to leave it unrestricted. Preferably the plunger Illd carries a disc I08 adapted to close the port 39 completely so that the pilot can cut off the fuel supply at will in case of emergency or when the engine is to be stopped. I

A further manual control is provided by a valve I It in the passage 86 urged onto its seat by a spring H2 and connected to the linkage act by a link IIE. The link lid is pivoted to. one end of a bellcrank lever i It, the other end of which is slidable on the stem of the valve IIIi and-is adapted to engage a nut M8 on the end thereof. This arrangement provides a lost mo tion connection so that the plunger I85 can be 7 operated as described above without affecting the for this purpose a fuel-nieteringead economizer is employed. In this device a calibrated by-pass I251: around metering orifice 30 connects the unetered fuel in chamber 28 with the metered'fuel the unmetered fuel.

The end of the economizer valve I25remote from the diaphragm assembly i3I carries a plunger MI slidably mounted in a cylinder I43;

provided.

' As the power output of the, engine increases, by opening the throttle or otherwise, the fuel deliv-- ered to the engine increases and consequently the.

fuel metering differential pressure increases. The fuel metering difierentlal pressure, that is the differential in the pressures in chambers 28 and M, acting on the economizer diaphragm I3! tends to open the economizer valve I25. When the fuel differential pressure equals or exceeds a predetermined value the force of spring I29 will be over- 1 It will be observed that a small orifice I23 extends through the diaphragm dIi to permit both diaphragm chambers 28 and M to fill with fuel simultaneously. The size of this orifice is proportioned in such a manner as not 'to have any materially bad effect on the operation of the device. In the event that the fuel control body which includes the fuel meteringjets 29. 30, the economlzer valve structure I25, fuel chamber I2! and the fuel outlet, are mounted in a plane parallel to and displaced from the axis of the-diaphragmpnd inlet valve control assembly. the fuel can, if desired, be taken from the lower end of chamber 28 and passed upwardly through the fuel control body. In this event the orifice I23 should be positioned to connect chamber 23 with chamber 521 at the upper end thereof, and the chamber 821 should be vented to chamber M at the upper end thereof. In order tosubject chamber 36 to the pressure existing-in chamber I27, a

ent of the control of the pilot. Either of these conditions can be obtained as desired by inclusion or exclusion of the orifice 29 or by properly proportioning the-size of this orifice. For example, if the area of passage I25a is greater than that of orifice 29, orifice 28 functions as the sole restriction to fuel flow when valve I25 is open as at full power, and operation of plunger I04 has then no effect on the fuel flow. On'the other hand, if the restriction formed by the orifice 28 is omitted or the orifice is made larger than the combined areas of passages H511 and 30, fuel fiow is metered by these two passages and the pilot, through operation of plunger I04, may control the mixture both during normal and emergency operation.

Figure 3 illustrates a modified construction for controlling the fiow of fuel into the chamber 28 and as shown includes a chamber I42 receiving v.fuel from the pump through the pipe 28. Com-- munication between the chambers 28 and I42 is controlled by a poppet valve I44 seating on a 'tapered valve seat I46 and connected to the rod 50 to be controlled thereby. The valve I44 has.

its stem I48 connected to one end of a lever I50 which is pivoted at its center in the chamber 25 I42 and has its opposite end formed as a weight I52. The weight I52 has substantially the same effective mass as the rod 50 and its related parts such as the disks 48 and 64 and serves to counterbalance any inertia effects on the rod 50 which might change the richness of the fuel mixture. Fuel pressure on the valve I44 is balanced by a. diaphragm I54 exposed on one side to the pres sure in the chamber l'42.and on its other side to the pressure in the chamber 28, through openings in a plate 158. The effective moment on the lever pivot of the diaphragm I54 is the same as that of the valve I44 and the diaphragm is connected to the weight I52 by a link I58 so as to balance out the effect of fuel pressure on the valve I44. I

The openings in plate I55 are preferably made small to provide a dashpot effect tending to damp any vibrations or any tendency of the valve I44 to flutter; If this, dashpot effect is not sufficient a second dashpot may be provided by a cylindrical extension I43 in the chamber I42 slidably receiving a piston I45 carried by "the valve stem I48. The piston may have a relatively loose fit in the cylinder, or a suitable by-pass may be providedvand since the cylinder will be filled with fuel a liquid dashpot is formed.

It will also be understood that many changes might be made in form and arrangement of parts and it is not intended that the scope of the invention shallbe limited to the forms shown and described nor otherwise thanby the terms of the appended claims. v 4

Certain of the subject, matter disclosed but not claimed herein is being claimed in my copending applications Serial Nos. 350,518 and 350,519, filed August 3, 1940, and Serial No. 362,572, filed October 24, 1840.

What is claimed is: i Y .1. A charge forming device comprising an inductlon passage having an air inlet, a venturi in said passage, a fuel conduit leading from a fuel source and discharging into said passage,

fuel metering means in' said conduit, manually operable means forvarying the effective area of said fuel metering means, a valve having a conical seat controlling the fuel conduit, a balancing diaphragm connected to said valve and subjected on opposite Sides to the pressure in said conduit anterior and posterior to the valvefor balancing the difierential pressure across said valve,

a control ro'dconnecte'd to said valve, a pair of diaphragms connected to said control rod, means for subjecting two of the faces of said diaphragms to the pressures at the venturi and air inlet respectively, means for subjecting the remaining two faces of the diaphragms to the fuel pressure in said conduit anterior and posterior to said fuel metering means, a by-pass around said fuelmetering means, and means responsive ,to the fuel pressures in said conduit anterior and posteriorto said fuel metering means for controlling said by-pass. 2. A charge forming device comprising an inductlon passage having an air inlet, a fuel conduit leading from a fuel source and discharging into said passage, fuel metering means in said conduit, manually operable valve means for varying the effective area of said fuel metering means, a main control valve assembly including through the passage for urging the valve toward open position, means responsive tothe differentie] in fuel pressure across said fuel metering means connected to said valve for urging the valv toward closed position, and means responsive to the fuel differential across said fuel metering means for varying the area of said fuel metering means. l

3. A charge forming device for an internal combustionengine comprising an air passage, a

fuel conduit for supplying fuel to the engine, a valve controlling said conduit, fuel metering meansin said conduit, means responsive to a differential pressure resulting from air, flow through the air passage for controlling said valve, means responsive to fuel pressures anterior and posterior to said fuel metering means for controlling said valve, manually operable valve means for varying the effective area of said metering means, and means responsive to the differential in the fuel pressures anterior and posterior to said fuel metering means for varying the effective area of said metering means, said first named valve being operative independently of said last named means.

4. A charge forming device for an internal combustion engine having an air passage, a fuel conduit receiving fuel from a source and discharging into the air, passage, 9, metering restriction in said conduit, manually operable means for varying the effective area of said restriction, a valve in said conduit,.means responsive to the differential in pressure at spaced points in the air passage and to the differential 0 in the fuel pressure on opposite sides of said metering restriction for controlling said valve, a by-pass around said metering restriction, a valve seat fixed in said by-pass, a valve cooperating with said fixed seat to control the fiow of fuel through the by-pass and adapted to close the adapted to open the valve at high rates of fuel' flow corresponding to periods of high power output.

5. In a charge forming device a fuelcontrol valve assembly comprising ajmember having a 7:, conical seat, avplungeri slidably mounted in said member and cooperating with said seat, means engaging the plunger and influenced by differential of fluid pressures at spaced points to conthe position control means and the plunger, and

a casing surrounding the valve assembly, said valve assembly being mounted in the casing as a unit to permit removal of the casing without altering the adjustment of the plunger with reference to its seat.

6. In a charge forming device having a casing, a fuelcontrol valve assembly comprising a member having a conical seat,a plunger cooperating with said seat, fluid pressure responsive means connected to said plunger for positioning the same with reference to the seat, and a balance diaphragm connected to said plunger and to said member and subjected onopposite sides to the fuel pressures anterior and posterior to said seat, said member, plunger, and balancing diaphragm being thereby insertible into the easing as a unit. v

7. The invention defined in claim 1 comprising in addition a counterweight connected to said control rod for balancing the inertia of said control rod assembly.

8. The invention defined in claim 2 comprising in addition a counterweight and a dashpot associated with said valve for respectively bal ancing inertia effects and damping oscillations of the valve.

9, In a charge forming device' for an internal combustion engine having an air passage, means in saidair passage for creating an air differential pressure in response to flow therethrough, a fuel conduit for supplying fuel to the engine, arearestricting means in said conduit for creating a fuel differential pressure in response to fuel fiow' therethrough, a fuel valve for variably controlling the fuel flow to the engine, and dia-- phragm means responsive to said air and fuel differential pressures for controlling the said fuel valve: the combination therewith of a valve for varying th effective area of the area restricting means to thereby vary the ratio between the rate of fuel flow therethrough and the fuel differential pressure, means operable only when the fuel difierential exceeds a predetermined relatively high value for operating said yalve comprising a diaphragm operably connected to the valve and subjected to thesaid fuel differential pressure, and manually operable means separate from said valve for varying the effective area of the area restricting means independently of said valve.

10. A charge forming device comprising an induction passage having an air inlet, a venturi in said passage, a fuel conduit leading from a fuel source and discharging into said passage,

sponsive to the fuel pressures in said conduit anterior and posterior to said fuel metering means for controlling said by-pass.

11. In a charge forming device for an internal combustion engine having an air passage, a throttle in'the passage, an. air differential pressure creating means in the passage anterior to the throttle, a fuel conduit receiving fuel from a source and supplying itto the engine,'fuel metering means in said conduit for creating a fuel difierential pressure in said conduit upon fiow of fuel therethrough, valve means for controlling the flow of fuel through the conduit, a pluralityof diaphragms connected to the valve means foroperating the same, means for subjecting the diaphragms to the air and fuel differential pressures, a valve forvarying the effective area of the fuel metering means, a diaphragm operably connected to thevalve, and fuel passages interconnecting the last named diaphragm and the fuel conduit for transmitting th said differential fuel pressure to the last named diaphragm, said diaphragm operated valve being inoperative at low values of fuel differential pressurescorresponding to low power output and beingvarranged to open when the differential fuel pressure exceeds a predetermined value corresponding to a relatively high power 'output of the engine.

12. In a charge forming device for an internal combustion engine, an air passage for supplying air to the engine, a fuel conduit for supplying fuel to the engine, a metering restriction in the conduit, fuel valve means for controlling the flow of fuel through said conduit, diaphragm means operably connected to said valve means by-pass around ,said metering restriction and having a fixed valve seat thereim'a valve cooperating with said seat for controlling, said by,-

fuel metering means in said conduit, manually pass, a spring yieldingly holding said by-pass valve in a closed position with a positive force, and pressure responsive means directly subject'- ed to the fuel pressures in said conduit on 0pposite sides of the metering restriction for opening the by-pass valve against the force ofthe spring when the difierentialinsai'd fuel pressures exceeds a predetermined valueto thereby increase the richness of the mixture at high power outputs.

13. A fuel supplying device for an internal combustion engine comprising a fuel pump, a

conduit receiving fuel under pressure from the pump and delivering it to theefigine, manually variable metering means in said conduit for varying the richness of the 'mixture delivered to the engine during periods of low power output, a fuel by -pass around said manually variable metering means, a valve normally closing said by-pass, and means responsive to the dif-v ferential of the fuer pressures in said conduitanterior and posterior to said variable metering means for moving said valve toward open position when the differential pressur exceeds a predetermined value to thereby increase the richness of the mixture at high power outputs.

14. The invention defined in claim 13 comprising in addition a dashpot associated with the bypass valve to damp out oscillations imparted thereto.

15. A carburetor having a fuel supply passage including a metering orifice fixed against orifice area varying movementAin response to changes aspects stant fuel air ratio, economizer means for effecting an increased fuel fiow through said fuel supphragms, one responsive to changes in said difanother normally balancing said first mentioned diaphragm and acted upon by fuel pressures on opposite sides of said orifice, and means movable proportionally with and responsive to changes in the differential of pressures 'on opposite sides of said orifice for unbalancing said last mentioned diaphragm and effecting displacement of said valv to increase the fuel flow through said valve to enrich the mixture and restore the balance of said diaphragms in the new position of the valve.

16. A carburetor having a fuel supply pas sage including a metering. orifice fixed against orifice area varying movement in response to changes in engine operation, an air supply passage including means upstream from the throttle for creating a differential of pressures proportional to air flow, a fuel valve in said fuel supply passage movable to vary th supply of fuel to said orifice means and normally balanced by opposing pressures of unmetered fuel being delivered to said orifice means, valve actuating means responsive to changes in said differential of pressures in said air passage and normally balanced by fuel pressures on opposite sides of said orifice for maintaining a substantially convvfeijential of pressures in said air passage and I ply passage to enrich the mixture and controlled by changes in the said fuel pressures on opposite sides of the orifice, and pressure responsive means for modifying the action of said differ; entials of pressures on said actuating means and on said economizer means in accordance with variations in the density of the air at different i altitudes. v

17. A carburetor having a fuel supply conduit including a main metering orifice fined against orific area varying movement in response to changes in engine operation and an economizer orifice in parallel with said main orifice, an air supply passage including means for creating a differential of pressures proportional toair flow, a. fuel inlet valve in said fuel supply conduit, valv actuating means including a diaphragm responsive to the differential of pressures in said air passage and also including a diaphragm acted upon by metered and unmetered fuel, and an economizer valve for efiecting an additional-flow of metered fuel and controlling the operation of 

